1.\" Copyright (c) 1985, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd July 13, 2020 29.Dt ARP 8 30.Os 31.Sh NAME 32.Nm arp 33.Nd address resolution display and control 34.Sh SYNOPSIS 35.Nm 36.Op Fl -libxo Ar options 37.Op Fl n 38.Op Fl i Ar interface 39.Ar hostname 40.Nm 41.Op Fl -libxo Ar options 42.Op Fl n 43.Op Fl i Ar interface 44.Fl a 45.Nm 46.Fl d Ar hostname 47.Op Cm pub 48.Nm 49.Fl d 50.Op Fl i Ar interface 51.Fl a 52.Nm 53.Fl s Ar hostname ether_addr 54.Op Cm temp 55.Op Cm blackhole No \&| Cm reject 56.Op Cm pub 57.Nm 58.Fl S Ar hostname ether_addr 59.Op Cm temp 60.Op Cm blackhole No \&| Cm reject 61.Op Cm pub 62.Nm 63.Fl f Ar filename 64.Sh DESCRIPTION 65The 66.Nm 67utility displays and modifies the Internet-to-Ethernet address translation 68tables used by the address resolution protocol 69.Pq Xr arp 4 . 70With no flags, the program displays the current 71.Tn ARP 72entry for 73.Ar hostname . 74The host may be specified by name or by number, 75using Internet dot notation. 76.Pp 77Available options: 78.Bl -tag -width indent 79.It Fl -libxo 80Generate output via 81.Xr libxo 3 82in a selection of different human and machine readable formats. 83See 84.Xr xo_parse_args 3 85for details on command line arguments. 86.It Fl a 87The program displays or, if it is used with the 88.Fl d 89flag, deletes all of the current 90.Tn ARP 91entries. 92.It Fl d 93A super-user may delete an entry for the host called 94.Ar hostname 95with the 96.Fl d 97flag. 98If the 99.Cm pub 100keyword is specified, only the 101.Dq published 102.Tn ARP 103entry 104for this host will be deleted. 105.Pp 106Alternatively, the 107.Fl d 108flag may be combined with the 109.Fl a 110flag to delete all entries. 111.It Fl i Ar interface 112Limit the operation scope to the 113.Tn ARP 114entries on 115.Ar interface . 116Applicable only to the following operations: 117display one, display all, delete all. 118.It Fl n 119Show network addresses as numbers (normally 120.Nm 121attempts to display addresses symbolically). 122.It Fl s Ar hostname ether_addr 123Create an 124.Tn ARP 125entry for the host called 126.Ar hostname 127with the Ethernet address 128.Ar ether_addr . 129The Ethernet address is given as six hex bytes separated by colons. 130The entry will be permanent unless the word 131.Cm temp 132is given in the command. 133If the word 134.Cm pub 135is given, the entry will be 136.Dq published ; 137i.e., this system will 138act as an 139.Tn ARP 140server, 141responding to requests for 142.Ar hostname 143even though the host address is not its own. 144In this case the 145.Ar ether_addr 146can be given as 147.Cm auto 148in which case the interfaces on this host will be examined, 149and if one of them is found to occupy the same subnet, its 150Ethernet address will be used. 151.Pp 152If the 153.Cm reject 154keyword is specified the entry will be marked so that traffic to 155the host will be discarded and the sender will be notified the 156host is unreachable. 157The 158.Cm blackhole 159keyword is similar in that traffic is discarded but the sender is 160not notified. 161These can be used to block external traffic to a host without 162using a firewall. 163.It Fl S Ar hostname ether_addr 164Is just like 165.Fl s 166except any existing 167.Tn ARP 168entry for this host will be deleted first. 169.It Fl f Ar filename 170Cause the file 171.Ar filename 172to be read and multiple entries to be set in the 173.Tn ARP 174tables. 175Entries 176in the file should be of the form 177.Pp 178.Bd -ragged -offset indent -compact 179.Ar hostname ether_addr 180.Op Cm temp 181.Op Cm blackhole No \&| Cm reject 182.Op Cm pub 183.Ed 184.Pp 185with argument meanings as given above. 186Leading whitespace and empty lines are ignored. 187A 188.Ql # 189character will mark the rest of the line as a comment. 190.El 191.Sh SEE ALSO 192.Xr inet 3 , 193.Xr libxo 3 , 194.Xr xo_parse_args 3 , 195.Xr arp 4 , 196.Xr ifconfig 8 , 197.Xr ndp 8 198.Sh HISTORY 199The 200.Nm 201utility appeared in 202.Bx 4.3 . 203